Electron micrographs (SEM) courtesy of Kurt Buck, Dave Mellinger,
Dave Wright, and the "Dune Booming Crew" of
MBARI
(Monterrey Bay Aquarium Research Institute),
who donated their spare time to this effort.

Notice that the smoothness of the booming sand
grains appear to be somewhere between the Luddington beach sample
(squeaking sand) and the Sand Mountain sample (booming sand) shown in
Fig. 2 of the Contemporary Physics article (see Fig. 2 above in this
web page).